159 research outputs found

    Forces between electric charges in motion: Rutherford scattering, circular Keplerian orbits, action-at-a-distance and Newton's third law in relativistic classical electrodynamics

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    Standard formulae of classical electromagnetism for the forces between electric charges in motion derived from retarded potentials are compared with those obtained from a recently developed relativistic classical electrodynamic theory with an instantaneous inter-charge force. Problems discussed include small angle Rutherford scattering, Jackson's recent `torque paradox' and circular Keplerian orbits. Results consistent with special relativity are obtained only with an instantaneous interaction. The impossiblity of stable circular motion with retarded fields in either classical electromagnetism or Newtonian gravitation is demonstrated.Comment: 26 pages, 5 figures. QED and special relativity forbid retarded electromagnetic forces. See also physics/0501130. V2 has typos corrected, minor text modifications and updated references. V3 has further typos removed and added text and reference

    On the number of limit cycles of the Lienard equation

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    In this paper, we study a Lienard system of the form dot{x}=y-F(x), dot{y}=-x, where F(x) is an odd polynomial. We introduce a method that gives a sequence of algebraic approximations to the equation of each limit cycle of the system. This sequence seems to converge to the exact equation of each limit cycle. We obtain also a sequence of polynomials R_n(x) whose roots of odd multiplicity are related to the number and location of the limit cycles of the system.Comment: 10 pages, 5 figures. Submitted to Physical Review

    What is the true clinical relevance of Simkania negevensis and other emerging Chlamydiales members?

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    <i>Waddlia</i>   <i>chondrophila</i> and <i>Simkania negevensis</i> are emerging <i>Chlamydia-</i> related bacteria. Similar to the pathogenic organisms <i>Chlamydia pneumoniae</i> and <i>Chlamydia trachomatis,</i> these emerging bacteria are implicated in human genital infections and respiratory diseases. We used a screening strategy based on a newly developed <i>S. negevensis</i> -specific quantitative real-time PCR (qPCR) and a pan- <i>Chlamydiales</i> qPCR. We could not detect <i>S. negevensis</i> in 458 respiratory, genitourinary, cardiac and hepatic samples tested. One urethral swab was positive for <i>W. chondrophila.</i> We observed a low prevalence of <i>Chlamydiales</i> in respiratory samples (1/200, 0.5%), which suggests that <i>C. pneumoniae</i> is an uncommon respiratory pathogen. Furthermore, we screened 414 human serum samples from Switzerland, England and Israel and observed a low prevalence (<1%) of exposure to <i>S. negevensis.</i> Conversely, humans were commonly exposed to <i>W. chondrophila,</i> with seroprevalences ranging from 8.6% to 32.5%. <i>S. negevensis</i> is not a clinically relevant pathogen, but further research investigating the role of <i>W. chondrophila</i> is needed

    Sequential administration of temozolomide and fotemustine: Depletion of O6-alkyl guanine-DNA transferase in blood lymphocytes and in tumours

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    Background: The DNA repair protein O6-alkylguanine-DNA alkyl transferase (AT) mediates resistance to chloroethylnitro-soureas. Agents depleting AT such as DTIC and its new analogue temozolomide (TMZ) can reverse resistance to chloro-ethylnitrosoureas. We report the results of a dose finding study of TMZ in association with fotemustine. Patients and methods: Twenty-four patients with metastatic melanoma or recurrent glioma were treated with escalating dose of oral or intravenous TMZ ranging from 300 to 700 mg/m2, divided over two days. Fotemustine 100 mg/m2 was given intravenously on day 2, 4 hours after TMZ. AT depletion was measured in peripheral blood mononuclear cells (PBMCs) and in selected cases in melanoma metastases and was compared to TMZ pharmacokinetics. Results: The maximum tolerated dose (MTD) of TMZ was 400 mg/m2 (200 mg/m2/d) when associated with fotemustine the 2nd day with myelosuppression as dose limiting toxicity. The decrease of AT level in PBMCs was progressive and reached 34% of pretreatment values on day 2. There was however wide interindividual variability. AT reduction was neither dose nor route dependent and did not appear to be related to TMZ systemic exposure (AUC). In the same patients, AT depletion in tumour did not correlate with the decrease of AT observed in PBMCs. Conclusions: PBMCs may not be used as a surrogate of tumour for AT depletion. Further study should concentrate on the pharmacokinetic pharmacodynamic relationship in tumour to provide the basis for individually tailored therap

    Elements Discrimination in the Study of Super-Heavy Elements using an Ionization Chamber

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    Dedicated ionization chamber was built and installed to measure the energy loss of very heavy nuclei at 2.7 MeV/u produced in fusion reactions in inverse kinematics (beam of 208Pb). After going through the ionization chamber, products of reactions on 12C, 18O targets are implanted in a Si detector. Their identification through their alpha decay chain is ambiguous when their half-life is short. After calibration with Pb and Th nuclei, the ionization chamber signal allowed us to resolve these ambiguities. In the search for rare super-heavy nuclei produced in fusion reactions in inverse or symmetric kinematics, such a chamber will provide direct information on the nuclear charge of each implanted nucleus.Comment: submitted to NIMA, 10 pages+4 figures, Latex, uses elsart.cls and grahpic

    Collapse of the N=28 shell closure in 42^{42}Si

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    The energies of the excited states in very neutron-rich 42^{42}Si and 41,43^{41,43}P have been measured using in-beam γ\gamma-ray spectroscopy from the fragmentation of secondary beams of 42,44^{42,44}S at 39 A.MeV. The low 2+^+ energy of 42^{42}Si, 770(19) keV, together with the level schemes of 41,43^{41,43}P provide evidence for the disappearance of the Z=14 and N=28 spherical shell closures, which is ascribed mainly to the action of proton-neutron tensor forces. New shell model calculations indicate that 42^{42}Si is best described as a well deformed oblate rotor.Comment: 4 pages, 3 figures, accepted for publication in Phys. Rev. let

    Description of the Main Features of the Series Production of the LHC Main Dipole Magnets

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    The series production of the LHC main dipole magnets was completed in November 2006. This paper presents the organization implemented at CERN and the milestones fixed to fullfil the technical requirements and to respect the master schedule of the machine installation. The CERN organization for the production follow-up, the quality assurance and the magnet testing, as well as the organization of the three main contractors will be described. A description of the design work and procurement of most of the specific heavy tooling and key components will be given with emphasis on the advantages and drawbacks
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